This invention relates to a system for vertically guiding a top driven drilling machine for use in a derrick. More particularly, the invention includes a spring mounted means for cooperating with a guide track to resist torque generated loads of a drill motor when drilling a well.
Conventional rotary drilling requires a rotary table, a motor mounted on the rig floor for rotating the table, a kelly and a kelly bushing. These drilling systems are being replaced by "top drive" drilling machines which rotate a drill string from above the rig floor using a drilling motor incorporated with a swivel bearing supported by a traveling block. This later drill motor-swivel bearing combination will herein be referred to as a power swivel.
A power swivel can be installed in a standard derrick or mast, hereafter referred to as a derrick. The drilling motor is connected to the drill string by a cylindrical stem or sub assembly extending downwardly from the drilling motor. Drilling is accomplished by the powered rotation of a suspended string of drill pipe. A cutting tool or bit is at the bottom end of the drill string which, through the rotational energy supplied by the power swivel, cuts through the earth's formations and deepens the well.
It is well known to mount a power swivel onto a carriage for support within a derrick. Rollers are rigidly mounted onto the carriage with the carriage guided by a pair of parallel rails or tracks vertically aligned along the axis of the derrick. Unlike conventional drilling machines where the drill motor is located on the rig floor, the tracks for top drive drilling machines must react to the torque loads generated by the drill motor during drilling. Drill motors up to 1000 HP are used and can develop intermediate torque up to 32000 ft-lbs. (43400 Joules) or more.
A guide system for the power swivel is needed to reduce impact loading and to allow for small abberations in the track. In the manufacture of the beams used for the track, it is not possible to maintain the same parallel distance between flanges or opposing sides of a beam. For this reason, if the rollers were spaced in such a manner as to contact the sides of the track at any one position on the track, there would be other positions where they would either not be in contact with both sides of the track or they would be too wide to fit in the track. If the space were not as wide as required for the rollers, the loads generated on the rollers by forcing them into that space would be great and would most assuredly lead to the untimely failure of the rollers. For this reason, it has been the practice in the past to space the rollers such that there is always some gap between the rollers and the flanges or sides of the track.
Leaving a gap between the rollers and the track causes the rollers to be subjected to impact loading. When the rollers are not directly against the track, any load which tends to rotate the power swivel is not resisted, causing the power swivel to rotate freely for a brief period of time. It is well known rotational forces vary greatly as a well is being drilled resulting in substantial motion of the power swivel. When the power swivel rotates far enough, the rollers will come into contact with the track. The momentum which exists in the power swivel due to its rotational energy it has gained from its brief free rotation is subsequently dissipated very rapidly under these conditions and results in high forces being applied to the track and the rollers.
Accordingly, there is a need for an improved guide system for top drive drilling machines. The guide system needs to provide limited controlled rotation between the drill motor and the track so that the impact loading to the track is reduced. Our invention overcomes this problem by mounting each support roller onto a spring with the spring urging each roller into continuous contact with the track. With the rollers urged against the track and a yieldingly limited rotation of the power swivel frame provided, reduced loads pass into the structural support and impact on the rollers and track is reduced. If the rollers are urged into contact with the tracks by the use of springs as the power swivel rotates, the power swivel is constantly required to overcome the constantly increasing force of the springs. This deflection of the springs requires work thus steadily dissipating the energy over time as opposed to dissipating the energy very quickly. Accordingly, forces applied to the track and rollers are reduced and impact to the track and rollers would be eliminated.